Chinese President Xi Jinping met leaders of the United Arab Emirates on Friday to bolster China’s economic ties with a key ally of Saudi Arabia, just as Beijing is emerging as a critical partner for an increasingly isolated Iran.

The three-day visit by Mr. Xi to the U.A.E. comes at a crucial time for a region buffeted by Saudi-Iran tensions. Mr. Xi, like other Chinese leaders before him, has taken an evenhanded approach to the Middle East, courting both the Sunni Muslim Arab states led by Saudi Arabia and the U.A.E., as well...